This invention relates to apparatus for operating a vertically movable door of the type comprising an electric motor, a friction clutch comprising a driving member and a driven member, first transmission means connecting the motor with said driving member and second transmission means connecting said driven member with the door. The friction clutch has for its principal purpose to set an upper limit to the torque transmitted and thus to prevent the door from exerting an excessive pressure upon a person or an object caught between the lower edge of the descending door and the foot of the doorway. It is also known to supplement apparatus of this type with a braking mechanism arranged to act on said second transmission means, and means for automatically controlling said braking mechanism including means for sensing the rotation of a rotary part of said second transmission means, said sensing means being arranged to render the braking mechanism operative when the rate of rotation deviate upwards or downwards from a predetermined range. This system results in a checking of further motion of the door as soon as the slowing down of the rotation caused by an obstacle in the path of the descending door is sufficient to make the sensing means operate the braking mechanism. While this action is desirable for safety reasons, the known system has the disadvantage that the motor will continue operating the driving member of the friction clutch the driven member of which is kept at a standstill by the braking mechanism, until somebody pushes the stop button to switch off the motor, or until the overload switch of the motor is released by the action of the overload caused by the operation of the slipping friction clutch.